One solution, perhaps, is if Lemmy users were better able to overcome the inertia of moving Communities, Instances, accounts, etc. Essentially to be a moving target for anyone who might want to cause harm. DDoSing lemmy.world? Okay, but we're all on lemmy2.world now. Spamming a Community? Oh, you mean that one we all left?
I'm not criticizing others, because I'm as guilty of it any anyone, but it might be better if we realized that our usernames are meaningless, there's no Karma, our comment histories are full of ephemeral observations with only a very specific relevance. It wouldn't really matter if - worst case scenario - everything was deleted. I realise this wouldn't sound acceptable to new users, but since many of us on instances run by one person as a hobby, that might happen anyway.
(As I was typing this, someone just replied to a 17 days old comment I made, so maybe this is all rubbish)